In forming or relining dentures, a technician first makes palate and gum impressions of a patient's mouth and then from these, forms positive models of dental "stone" (calcined gypsum). In relining, a layer of "curable" plastic, such as acrylic resin which replaces the vulcanizable "soft rubber" of earlier days, is then lodged between each respective denture and its model, and allowed to harden to a permanent, pressure-formed configuration. This is done by clamping these assembled pieces embodied in a mass of molding material such as plaster of Paris, in a positioning press and placing the press and workpiece in a pressure chamber, sometimes at elevated temperature, for a short "cure", such as ten minutes.
However, in contrast to earlier dental flasks which could be pour-filled with slow-curing denture material, the present relining press must be quickly brought to final (pressure) alignment position because the acrylic relining material upon catalyst addition begins to harden almost immediately. Thus the workpiece-contacting upper and lower positioning plates of the press must assume a mutually parallel "final" position at once, and maintain it constant during the curing period. In contrast, it has been observed in the past, that in response to (unrealized) unequal clamping pressure against the upper plate, (i.e. at a particular post or tensioning nut) the parallel contact plates may gap apart (slightly) and such gap is transmitted to the workpiece so that the cured dentures may (when closed) thus occlude incompletely, in the front or back as the case may be. Since such misalignment may go unnoticed while the curing elements become set in the press, to correct it, a whole new relining job must then be done.
Various attempts have been made to overcome this problem, including making the entire jig into an enclosed assembly, or using a three post, open construction, as well as making the contact plates of heavy metal. Nevertheless, none have proven completely satisfactory, partly due to such unpredictable "gapping" of the final product, part of which may be due to the length of time required to assemble and align the press with the workpiece, and part of which may be due to pressure bending of the contact plate(s) of the jig or press. A prior art example is U.S. Pat. No. 4,218,205 to Beu.